The present invention relates to a two-stage electrohydraulic servo valve with a first stage, which operates as pilot stage and includes a movable nozzle tube, and a second stage which operates as power stage.
In modern hydrosystems engineering, particularly high demands often are placed on the operating behavior of the installed hydraulic components within such hydrosystem. In particular, the installed hydraulic components are meant to regulate certain hydraulic volume flows and pressures with high precision corresponding to given control signals. Valves suitable for this purpose, in particular continuous valves, allow to permit a continuous transition of the switching positions of the valve. In said continuous valves, an electrical input signal correspondingly is converted into a hydraulic output signal for actuating the continuous valve. One category of the continuous valves includes the well-known servo valves, which allow a highly precise and above all continuous adjustment of the valve switching position, which in particular in modern aircraft technology is regarded as a basic prerequisite.
From the prior art, so-called two-stage servo valves are known, whose power stage includes a control piston which in its starting position normally prevents the volume flow between a pressure input and a pressure output channel. Inside the power stage, the control piston is in a pressure equilibrium. For actuating the power stage, i.e. for the controlled deflection of the control piston, which permits a volume flow between an input channel and an output channel, an electrically actuatable pilot stage is used, which effects the required deflection of the control piston.
One embodiment of the pilot stage operates according to the known nozzle tube principle. For this purpose, a nozzle tube supplied with hydraulic fluid is movably articulated in a pivot point of the pilot stage. The pressure equilibrium of the control piston of the power stage in the zero-point position can be influenced by corresponding control lines connected to the nozzle tube. By means of the electrical control signals output to the pilot stage, the nozzle tube can be swivelled to and fro between the two control lines, whereby the pressure can be increased selectively to certain points of the control piston of the power stage. The change in pressure enforces a movement of the control piston out of the zero-point position, which corresponds to a continuous switching transition of the valve.
In the pilot stages known so far, the pressure supply of the nozzle tube is achieved by an external tube conduit, whose connection point is susceptible to the vibrations, pressure fluctuations and zero-point shifts occurring in the valve during the operation.